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https://issues.apache.org/jira/browse/KAFKA-8677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16970409#comment-16970409
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ASF GitHub Bot commented on KAFKA-8677:
---------------------------------------

guozhangwang commented on pull request #7613: KAFKA-8677: Simplify the 
best-effort network client poll to never throw exception
URL: https://github.com/apache/kafka/pull/7613
 
 
   
 
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> Flakey test 
> GroupEndToEndAuthorizationTest#testNoDescribeProduceOrConsumeWithoutTopicDescribeAcl
> ------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-8677
>                 URL: https://issues.apache.org/jira/browse/KAFKA-8677
>             Project: Kafka
>          Issue Type: Bug
>          Components: core, security, unit tests
>    Affects Versions: 2.4.0
>            Reporter: Boyang Chen
>            Priority: Blocker
>              Labels: flaky-test
>             Fix For: 2.4.0
>
>
> [https://builds.apache.org/job/kafka-pr-jdk11-scala2.12/6325/console]
>  
> *18:43:39* kafka.api.GroupEndToEndAuthorizationTest > 
> testNoDescribeProduceOrConsumeWithoutTopicDescribeAcl STARTED*18:44:00* 
> kafka.api.GroupEndToEndAuthorizationTest.testNoDescribeProduceOrConsumeWithoutTopicDescribeAcl
>  failed, log available in 
> /home/jenkins/jenkins-slave/workspace/kafka-pr-jdk11-scala2.12/core/build/reports/testOutput/kafka.api.GroupEndToEndAuthorizationTest.testNoDescribeProduceOrConsumeWithoutTopicDescribeAcl.test.stdout*18:44:00*
>  *18:44:00* kafka.api.GroupEndToEndAuthorizationTest > 
> testNoDescribeProduceOrConsumeWithoutTopicDescribeAcl FAILED*18:44:00*     
> org.scalatest.exceptions.TestFailedException: Consumed 0 records before 
> timeout instead of the expected 1 records
> ---------------------------
> I found this flaky test is actually exposing a real bug in consumer: within 
> {{KafkaConsumer.poll}}, we have an optimization to try to send the next fetch 
> request before returning the data in order to pipelining the fetch requests:
> {code}
>                 if (!records.isEmpty()) {
>                     // before returning the fetched records, we can send off 
> the next round of fetches
>                     // and avoid block waiting for their responses to enable 
> pipelining while the user
>                     // is handling the fetched records.
>                     //
>                     // NOTE: since the consumed position has already been 
> updated, we must not allow
>                     // wakeups or any other errors to be triggered prior to 
> returning the fetched records.
>                     if (fetcher.sendFetches() > 0 || 
> client.hasPendingRequests()) {
>                         client.pollNoWakeup();
>                     }
>                     return this.interceptors.onConsume(new 
> ConsumerRecords<>(records));
>                 }
> {code}
> As the NOTE mentioned, this pollNoWakeup should NOT throw any exceptions, 
> since at this point the fetch position has been updated. If an exception is 
> thrown here, and the callers decides to capture and continue, those records 
> would never be returned again, causing data loss.



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